Why doesnt my cat prefer me?

I clean his litter, i feed him, give him treats, and teh occional time he wants to cuddle with me i cuddle him. but he now sleeps with my roommate (he used to sleep with me, then moved to the foot of my bed now fully with her all night) and she doesnt do any feeding, cleanin, or playing.... in fact she kinda terrorizes him... what did i do wrong?? why doesnt he love me anymore?